Such optical switch matrices are known. On Feb. 10, 1995, during a workshop of Eindhoven University of Technology in the Netherlands Siemens presented an 8.times.8 optical switch matrix named "8.times.8 Modulaufbau," which consists of an array of sixteen juxtaposed 1.times.8 switches on a long rectangular InP-substrate and optical fibres (embedded in a product of AT&T called "Optiflex.TM." and bent through an angle of 180.degree.) for connecting the switches. Eight of said 1.times.8 switches are each used as an input channel which branches into in eight channels. Each of these branched channels is connected to one of the merging channels of the remaining eight 1.times.8 switches (or, more accurately, 8.times.1 switches), in such a manner that an input signal in one of the input channels can be switched to any one of the output channels.
Said optical switch matrix has a length of more than 300 mm and a width of at least 50 mm, which is very large, especially in an industry where small size is, in many cases, of the essence. A reason for these considerable dimensions is that the optical fibres, which are usually made of glass, can only be bent to a certain extent. The minimal bending radius for glass fibres is about 25 mm. If smaller radii are used, the glass fibre may break or the optical loss within the fibre may increase to an unacceptably high level. As mentioned, in said optical switch matrix the fibres are bent through an angle of 180.degree.. Consequently, the minimum width of the matrix exceeds 50 mm.